The present invention generally relates to an electrical switch and more particularly, to an electrical snap switch which is adapted to selectively close or open an electric path through snap action.
Conventionally, as an electrical switch of the above described type, there has been proposed an arrangement as shown in FIG. 1, in which a forward end of a receiving piece 2 is supported by a common terminal 1 through an edge contact (as at a supporting point A), while a rear end of a movable piece 3 is supported by a corresponding rear end of the receiving plate 2 also through an edge contact (as at a supporting point B) for engagement with a pushbutton 4, with a movable spring 5 being held between a portion in the vicinity of a contact of the movable piece 3 and the common terminal 1 (as at engaging points C and D).
In the known snap switch as referred to above, upon depression of the pushbutton 4, the receiving plate 2 is rotated counterclockwise about the supporting point A, with a pivotal movement of the movable piece 3 about the supporting point D in a counterclockwise direction, and when the supporting point B passes through a line connecting the engaging points C and D, the movable piece 3 is reversed downwardly through a snap action, so that a movable contact 6 is changed over from a normally closed stationary contact 7b to a normally open stationary contact 7a. On the other hand, when the pushbutton 4 is released from the depressing force, the movable contact 6 is changed over from the contact 7a to the contact 7b in the reverse order to the above.
The prior art switch as described above, however, has such disadvantages that, since the receiving plate 2, the movable piece 3 and the movable spring 5 are combined with each other for engagement with the common terminal 1, holding and assembling of such parts during assembly of the switch are difficult, thus requiring much time and labor therefor.
Moreover, as shown in FIGS. 2 and 3, since the supporting point A is positioned at an outside lower portion of a triangle formed by connecting the engaging point C in a free state, the engaging point C' in a functioning state and the engaging point D, large forces are required both for the functioning and restoration, and therefore, the switch can not be adapted to function at a small load. Furthermore, due to the fact that a functioning distance L between the supporting point B in the free state and the supporting point B' in the functioning state can not be reduced by positioning the point B and the point D close to each other because of the presence of thicknesses of the common terminal 1 and receiving plate 2 therebetween, it is difficult to provide an electrical snap switch with a high sensitivity.
In connection with the above, relationship of forces at the points B and C is illustrated in FIG. 3, in which Fs represents a force acting on the movable piece 3 by the movable spring 5, Fe denotes a component force produced in a longitudinal direction of the movable piece 3, Fo shows a force for restoring the receiving plate 2, i.e. the restoring force of the pushbutton 4, Fa is a force directed towards the supporting point A of the receiving plate 2, and Fc represents a force for pressure contact towards the normally closed contact.